The invention relates to improvements in vehicle brake systems.
A brake system of this type is known from German Offenlegungsschrift No. 29 21 275, for example, which addresses the problem that the sum of the pedal force and servo force is always operative in a brake system having a brake booster. Very high brake pressures can arise in the individual brake circuits, especially in panic stops. The entire brake system must be dimensioned accordingly; that is, the individual brake circuits and the components belonging to them, such as the brake line and the wheel brake cylinders, must be capable of withstanding not only the high pedal pressures but also full boosting by the brake booster. This means a considerably greater consumption of material; in addition, the individual seals are subjected to considerable loads. German Offenlegungsschrift No. 29 21 275 has therefore already proposed pressure reduction valves, which come into play at the instant that excessively high pressures arise. The effect of these pressure reduction valves is that further feeding of the brake booster stops, and the brake booster is bled via a return line. Problems arise with the 3/2-way valves shown there, especially in terms of keeping them tight. It has also proved unfavorable to bleed the brake booster immediately upon switching on the pressure reduction valve, because this pumps brake fluid unnecessarily into the supply container, from which it has to be withdrawn again later by the pump.